The present invention relates to a copper alloy with an improved composition and method of manufacturing the same. In particular, the invention relates to a copper alloy for electronic instruments suitable above all for the lead of electronic parts such as semiconductors etc. and which is excellent in strength, thermal and electric conductance, platability, solderability, bonding ability, corrosion resistance, heat resistance and processibility and the manufacturing method therefor. Namely, the alloy of the invention is an engineering material for the precision lead frame.
Various copper alloys have been utilized for the parts of electronic instruments, for example, the lead frame material of semiconductors (transistor, IC, LSI, VLSI, diode, etc.), heat sink material, the lead material of electronic parts, spring material of structural parts (connector, switch, relay, etc.) and different kinds of terminal materials. Recently, accompanying the miniaturization, high performance and high densification of the parts of electronic instruments, an alloy with higher performance has become necessary. Particularly, in the case the semiconductor, the high integration is startling, and, for the lead frame thereof, high strength and excellent radiation property (electric and thermal conductance) are needed. For this reason, in place of Fe 42-Ni or Fe 29-Ni 17-Co, a copper alloy excellent in electric and thermal conductance is desired.
The phosphor bronze (Cu-Sn type), which is a typical copper alloy excellent in strength as high as 50 to 70 kg/mm.sup.2 and used widely for the connector, relay, switch and terminal, is not necessarily suitable for the lead frame since the electroconductivity is as low as 10 to 20% IACS. Moreover, it is susceptible to stress corrosion cracking and, more important, with lapse of time the bonding strength by soldering deteriorates, and the alloy shows a tendency to cause peeling off of Sn or Sn-Pb plating. For this reason, Cu-Fe type alloys having characteristics of 50 to 65% IACS of electroconductivity, 45 to 55 kg/mm.sup.2 of tensile strength and 2.5 to 10% of elongation, for example, C 194 (CU-2.4 wt.% Fe-0.12 wt.% Zn-P alloy) (hereinafter, wt.% is abbreviated as % simply) and C 195 (Cu-1.5% Fe-0.8% Co-0.6% Sn-P alloy) have come to be used. However, these alloys come to have a microstructure dispersed with a lot of Fe or compounds among Fe, Co and P. As a result, the microcracks are apt to occur at the time of precise bending molding of the lead portion during miniaturation, the bonding strength by soldering is poor, and the adhesion of Ag plating etc. is insufficient. Furthermore, there are Cu-Ni-Si type alloys having similar characteristics to the alloys described above, but these alloys also have the same problems.
With the alloys as described above, the deficiencies in the electric and thermal conductance and the moldability come into question in rapid miniaturization and high integration of the semiconductor and, at the same time, particularly since the surfacemount technology has gained power as a mount system of high density, the strength at the bonding portion by soldering shows a tendency to be deteriorated with the lapse of time, which is worrisome.
For the electronic instruments represented by the semiconductor, the following characteristics are needed:
(1) To be excellent in strength and electric and thermal conductance, in particular, to have more than 30% IACS of electroconductivity and more than 50 kg/mm.sup.2 of tensile strength in the use as a lead frame. More preferably, to have more than 70% IACS. Also, more than 60 kg/mm.sup.2 is needed for the lead frame of high density because of the narrow width of lead. These needs are intense also in uses other than the lead frame.
(2) To be able to keep the bonding strength by soldering as well as the solderability and the wettability with solder for a long period of time.
(3) To be excellent in platability.
(4) To have heat resistance, that is, to be able to keep the above mentioned strength even at 300.degree. to 400.degree. C.
(5) To have corrosion resistance, that is, to to be resistant to stress corrosion cracking and oxidation at high temperature.
(6) To be suitable for wire bonding.
(7) To be able to be manufactured economically.
As a result of extensive investigations in view of the above situation, a copper alloy for electronic instruments suitable above all for the lead of electronic parts such as semiconductors etc. and excellent in strength, radiation property, formability, platability, bonding strength by soldering, corrosion resistance, heat resistance, etc. and a method of manufacturing the same have been developed by the inventions.